Several Republican House incumbents lost tight races in the 2018 midterm election, but Maine's two-term Rep. Bruce Poliquin did so in historical fashion.

Poliquin's Democratic challenger Jared Golden was declared the winner Thursday in the first federal election in U.S. history to be decided by a "ranked-choice" voting system.

Poliquin was also the first incumbent to lose the seat in more than 100 years, The Associated Press reported. His loss flips another Republican House seat to the Democrats and leaves Maine Sen. Susan Collins as the lone Republican in Congress from New England.

Poliquin narrowly got the most votes on Election Day – with 46.1 percent to Golden's 45.9 – but because he didn't get more than 50 percent of the vote, Maine's new law kicked in. Independent candidates Tiffany Bond and William Hoar combined received about another 8 percent of the vote.

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Bob Hugin, the Republican candidate in the New Jersey Senate race, covers his eyes while giving a concession speech to his supporters at the Stage House Tavern in Mountainside, N.J., Tuesday, Nov. 6, 2018. Amy Newman, The Record, via AP

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In the new system, approved by Maine voters in 2016, a person votes for their favorite candidate and ranks the other candidates by their order of preference. If no candidate gets more than 50 percent of the vote, the last-place candidate gets knocked out and the ballots cast for them are reallocated based on an algorithm that factors the voters' preferences. That process continues until one candidate has a majority.

After the votes were adjusted, Poliquin, 65, lost his lead in what had been a four-way race on Election Day and the 36-year-old Golden was declared the winner.

Maine is the first state to use ranked-choice voting in a statewide election, the Portland Press Herald reported, although some cities use similar systems. Some other countries, including Australia and Ireland, also use variations of ranked-choice. Maine used the system in the state's June primaries.

Poliquin filed a lawsuit asking for a halt in the ranked-choice tabulation, arguing it is unconstitutional. U.S. District Judge Lance Walker declined Poliquin’s request to stop the count on Thursday morning. But he did not definitively rule on the constitutionality of the law, leaving open the possibility that it could still be overturned and Poliquin declared the winner.

"It is now officially clear I won the constitutional 'one-person, one-vote' first choice election on Election Day that has been used in Maine for more than one hundred years," Poliquin said in a statement. "We will proceed with our constitutional concerns about the rank vote algorithm."

Golden was confident he would overcome Poliquin's legal challenge and told reporters Thursday that he is the "majority consensus winner." The Marine Corps veteran vowed to work with Republicans to get things done in Washington rather than focus on investigations into the Trump administration. He also said he would not vote for current House Minority Leader Nancy Pelosi, D-Calif., for House Speaker.

Third-party and independent candidates often get a lot of votes in Maine. The state's voters approved ranked-choice voting in a referendum after nine of the previous 11 governors were elected without a majority of the vote.

For now, the ranked-choice voting system is used only in federal races and in statewide primary elections. It can't be used in the governor’s race or state legislative races because the state constitution explicitly says the winners in those races are determined by a plurality of the vote.

Democratic Gov.-elect Janet Mills, who won her primary with the ranked-counting system, has said she will try to amend Maine’s constitution so the system can be used in all elections.